Poly(biphenyl ether sulfone)s, in particular polyphenylsulfones (PPSU), are amorphous technopolymers which are materials of choice notably for the ultimate in toughness, with rather good stiffness, rather good chemical resistance, superior to most of commercially available transparent resins but lower than that of ultra-performance polymers like poly(aryl ether ketone)s.
Precisely, poly(aryl ether ketone)s, in particular polyetheretherketones (PEEK) and polyetherketoneketones (PEKK), offer an exceptional balance of technical properties, namely high melting point, excellent thermal stability, high stiffness and strength, good toughness and really excellent chemical resistance, including excellent resistance to chemicals after exposure to said chemical under stress (“environmental stress rupture resistance”).
However, for certain applications, a higher level of stiffness is required, which cannot be achieved with a poly(aryl ether ketone) taken alone, and, a fortiori, with a poly(biphenyl ether sulfone) taken alone. A known solution, among others, consists in incorporating a reinforcing filler to the neat polymer. Non limitative examples of reinforcing fillers include particulate fillers like nanoclays, and fibrous fillers like glass fibers and carbon fibers. Thus, for example, certain glass-filled PEEKs have been developed and found a certain commercial success.
Yet, as concerns said glass-filled PEEKs and more generally reinforced poly(aryl ether ketone)s, their high cost (which is due to the high cost of the poly(aryl ether ketone)s themselves), remains often dissuasive, refraining the skilled person from using them as widely as technically desirable for the encompassed applications (shaped articles), in particular when, a high initial stiffness is mandatory and must be retained inasmuch as possible after the shaped articles or at least some part(s) thereof are contacted, temporarily or permanently, with an aggressive chemical environment under stress.
There remains thus a strong need for a composition of matter exhibiting a level of properties (in particular of chemical resistance, and very particularly of environmental stress rupture resistance) as high or substantially as high as the one achieved with reinforced poly(aryl ether ketone)s, at a lower cost than that of said reinforced poly(aryl ether ketone)s.
The challenge appeared tricky for the Applicant, notably in view of the teachings of U.S. Pat. No. 4,804,724, as commented below.
U.S. Pat. No. 4,804,724, the whole content of which is herein incorporated by reference, describes unreinforced blends comprising a poly(aryl ether ketone) and a poly(biphenyl ether sulfone). As expected, these blends, at intermediate compositions (such as 50 parts of PPSU and 50 parts of PEEK), exhibit intermediate properties, in particular an intermediate stiffness (modulus) and an intermediate chemical resistance (including an intermediate environmental stress rupture resistance) in certain chemical environments (ethyl acetate, 1,1,1-trichloroethane, toluene and acetone) in the range between the (high) chemical resistance of the poly(aryl ether ketone) and the (substantially lower) chemical resistance of the poly(biphenyl ether sulfone). Thus, in short, the skilled in the art, in view of the teachings of U.S.'724, would have understood that replacing part of the poly(aryl ether ketone) contained in a poly(aryl ether ketone) composition, whatever reinforced or not, by a usually more cost-attractive polymer, in particular a poly(biphenyl ether sulfone), should not be an appropriate means to solve the complex problem of reducing the cost of the poly(aryl ether ketone) composition while at least substantially maintaining the chemical resistance conferred by the poly(aryl ether ketone).
U.S. Pat. No. 5,916,958 addresses the problem of improving the flame retardancy of poly(biphenyl ether sulfone) compositions, including but not limited to PPSU compositions; to solve this problem, a fluorocarbon polymer and titanium dioxide should be added to the poly(biphenyl ether sulfone)composition. Optionally, the poly(biphenyl ether sulfone) compositions of US'958 comprise further a poly(aryl ether ketone), including but not limited to PEEK and PEKK. Other optional ingredients include fibrous fillers like glass fiber, as well as particulate fillers such as wollastonite, talc, silica and the like. U.S. Pat. No. 5,916,958 does not disclose any composition that would specifically comprise a poly(biphenyl ether sulfone), a poly(aryl ether ketone and a fibrous filler, except comparative example N, which relates to a composition consisting of (i) 90 wt %, based on the total weight of the composition, of a polymer blend consisting of 85 parts by weight of a polyphenylsulfone (RADEL(r) R 5000 grade) and 15 parts by weight of a polyetheretherketone (VICTREX® PEEK grade 150 P), and (ii) 10 wt %, based on the total weight of the composition, of glass fiber. As earlier mentioned, this example is provided as comparative example, for the sole purpose of demonstrating that glass fiber makes it possible to achieve good heat release properties, even in the absence of fluorocarbon polymer and TiO2, but would cause unacceptable unscratched impact values. This disclosure is totally unrelated with the complex problem addressed by the present invention.